Ravenous Bugblatter Beast of Traal
The action of using a magic item is not the same action as casting a spell. They are 2 distinct and different actions.
True but irrelevant in this particular case. Let me give an example elsewhere. Say you had up Hex, which adds +d6 necrotic damage whenever you hit the target with an attack. That extra damage does not care if you hit with an attack with the Attack action, with the Cast a Spell action to attack with Booming Blade or Green Flame Blade, or with a reaction to make an Opportunity Attack. Or even with a bonus action if you were dual wielding or had Polearm mastery. Similarly, the limitations on a bonus action spell do not care what the action is used, you simply can not cast another spell during the same turn with the exception of a cantrip with a casting time of 1 action.
The magic item is casting the spell NOT YOU. It's the same as using a potion. The potion is giving the spell effect, NOT YOU. You are not using any verbal, somatic, or material components when you use a magic item. Ultimately it comes down to what your DM thinks.
Potions are a different category and have different rules, so I won't deal with that. But using a wad/staff specifically calls out in all their descriptions things like "While hold it, YOU can expend 1 charge as an action to cast the XX spell from it". In some, like the Wand of Magic Missiles it's even clearer "For 1 charge, you cast the 1st level version of the spell."
So where we are is that (a) the action type doesn't matter, and (b) you are the caster using an item.